nextzen.js prep

[hanbyul-here]

• move this repo to nextzen github account
• build the script with updated leaflet geocoder
• build with new lrm-mapzen (geocoder and lrm both have warning messages for users directly hitting Mapzen endpoint)
• point house styles to nextzen one
• resolve image asset url (https://github.com/mapzen/mapzen.js/blob/master/src/js/mapzen.js#L28)
• drop the current build CI
• change the attribution
• drop the unified api key check. (Delegate api key check to each component.)